Welding quality inspection device

Abstract

The welding quality inspection device according to the present invention is a device for checking the welding state at the welding part for electronic or mechanical connection in the lithium secondary battery. The welding quality inspection device is characterized in that it includes: a measuring unit, the measuring unit makes the resistance measuring probe contact the welding part, thereby obtaining data for deriving the resistance value of the welding part; and a controller, the controller communicates with the measuring unit, receives the data obtained from the measuring unit to determine the resistance value at the welding part, and determines whether a weak weld is performed at the welding part by comparing the determined resistance value with a threshold resistance value, wherein the measuring unit is configured so that the resistance measuring probe contacts each of one end and the other end of the welding part.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0026135, filed on Mar. 2, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a device for inspecting the welding state of a welding portion of an electronic or mechanical connection in a lithium secondary battery, and more particularly, to a device for inspecting whether a weak weld is made on a welding portion between electrode tabs and a welding portion between an electrode tab and an electrode lead. Background Art

[0003] Generally, unlike a primary battery that cannot be charged, a secondary battery means a battery that can be charged and discharged, and is widely used in electronic devices such as mobile phones, notebook computers, cameras or electric vehicles. In particular, a lithium secondary battery has a larger capacity than a nickel-cadmium battery or a nickel-metal hydride battery, and because of its high energy density per unit weight, the use of lithium secondary batteries is rapidly increasing.

[0004] In addition, lithium secondary batteries are classified according to the structure of an electrode assembly having a positive electrode / separator / negative electrode structure. Representative examples thereof include: a jelly roll electrode assembly in which a long sheet-type positive electrode and a negative electrode are wound with a separator interposed therebetween; a stacked electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween; and a stacked / foldable electrode assembly in which a double cell or a full cell is wound, in which a predetermined unit of positive and negative electrodes are stacked with a separator interposed therebetween.

[0005] In recent years, a pouch-type battery having a stacked or stacked / folded type electrode assembly embedded in a pouch-shaped battery case made of an aluminum laminate sheet has attracted much attention due to its low manufacturing cost and light weight, and its use is gradually increasing.

[0006] Lithium secondary batteries mainly use lithium oxides and carbon materials as positive electrode active materials and negative electrode active materials, respectively. Lithium secondary batteries include: an electrode assembly in which a positive electrode plate and a negative electrode plate coated with a positive electrode active material and a negative electrode active material, respectively, are placed with a separator therebetween; and an external material that seals and stores the electrode assembly together with an electrolyte.

[0007] At this time, a plurality of positive electrode tabs extending from a plurality of positive electrode plates and a plurality of negative electrode tabs extending from a plurality of negative electrode plates are formed in the electrode assembly, and the plurality of positive electrode tabs and the plurality of negative electrode tabs are respectively coupled to the positive electrode lead and the negative electrode lead by welding. Here, the plurality of positive electrode tabs and the plurality of negative electrode tabs form electrode tabs, and the positive electrode lead and the negative electrode lead form electrode leads.

[0008] Similarly, when the electrode tabs and the electrode leads are welded, welding defects may occur if weak welding is performed between the electrode tabs and between the electrode tabs and the electrode leads. Therefore, a process of inspecting whether there are welding defects caused by such weak welding is required.

[0009] Conventionally, in order to check welding defects caused by weak welding on a welding portion, the tensile strength is measured by pulling the welding portion in the opposite direction. However, when this method is used, the electrode tab or the electrode lead may be damaged during the process of measuring the tensile strength. Therefore, a comprehensive investigation cannot be performed.

[0010] Therefore, there is a need for a technique regarding an apparatus for inspecting a weak weld of a welded portion with excellent detection capability while allowing a comprehensive investigation. Summary of the invention

[0011] Technical issues

[0012] Therefore, the present invention is designed to solve the above problems, and an object of the present invention is to provide an apparatus for inspecting a weak weld of a welded portion with excellent detection capability while allowing a comprehensive investigation.

[0013] Technical Solutions

[0014] The welding state inspection device of the present invention for achieving the above-mentioned object is a device for inspecting the welding state in a welding part for electronic or mechanical connection in a lithium secondary battery, the device comprising: a measuring unit, the measuring unit being configured to obtain data for deriving the resistance value of the welding part by allowing a resistance measuring probe to contact the welding part; and a controller, the controller being configured to communicate with the measuring unit, determine the resistance value of the welding part by receiving the data obtained from the measuring unit, and determine whether weak welding is performed by comparing the determined resistance value with the threshold resistance value, wherein the measuring unit is configured to allow the resistance measuring probe to contact one end and the other end of the welding part.

[0015] In a specific example, if the determined resistance value exceeds the threshold resistance value, the controller determines that weak welding is performed.

[0016] In a specific example, the measuring unit includes: a flat bracket on which the object is mounted; an upper plate, which is configured to be located on an upper portion having a predetermined separation distance from the bracket and includes a plurality of through holes into which the resistance measuring probe can be inserted; a lower plate, which is configured to be located on a lower portion having a predetermined separation distance from the bracket and includes a plurality of through holes into which the resistance measuring probe can be inserted; a connecting unit, which is configured to allow the bracket, the upper plate and the lower plate to be connected to each other; and a pair of resistance measuring probes, which are configured to obtain data for determining a resistance value by contacting the welding portion.

[0017] In a specific example, a resistance measurement probe includes a current probe and a voltage probe.

[0018] In a specific example, upper and lower guide members for allowing the resistance measuring probe to be inserted into a correct position are coupled to the upper and lower plates, respectively.

[0019] In a specific example, the upper guide member and the lower guide member respectively have through holes into which the resistance measuring probe can be inserted, the through hole of the upper guide member and the through hole of the upper plate are located in a straight line, thereby allowing the resistance measuring probe to pass through the through hole to approach the upper surface of the welding portion, and the through hole of the lower guide member and the through hole of the lower plate are located in a straight line, thereby allowing the resistance measuring probe to pass through the through hole to approach the lower surface of the welding portion.

[0020] In a specific example, the coupling unit includes a coupling rod and a coupling screw.

[0021] In a specific example, the bracket, upper plate and lower plate each have coupling holes at four edge portions, and when the coupling rod passes through the coupling holes formed on the upper plate, bracket and lower plate in sequence, the upper plate, bracket and lower plate are coupled.

[0022] In a specific example, the device further includes a compression spring for adjusting a separation distance between the bracket and the upper plate and a separation distance between the bracket and the lower plate, wherein the connecting rod is configured to be insertable into a hollow portion of the compression spring.

[0023] In a specific example, the controller includes a threshold resistance value setting program for setting the threshold resistance value by processing data obtained for a sample group in a statistical scheme.

[0024] In a specific example, the resistance values ​​determined from the data obtained for the sample group form a normal distribution curve.

[0025] In a specific example, the inspection device according to the present invention further includes an output unit configured to display the data obtained from the measuring unit and the resistance value of the welding portion determined by the controller.

[0026] In a specific example, the inspection apparatus of the present invention further includes a power supply configured to apply power to the measurement unit, wherein the power is direct current (DC) power and is controlled by the controller.

[0027] Beneficial effects

[0028] According to the welding status inspection method described in the present invention, the resistance of the sample group is measured, and the threshold resistance value is set from the normal distribution curve of the measured resistance value, and when the resistance of the sample group and the welding part to be inspected is measured, the micro-resistance with a resolution of nanoohms to microohms can be measured, thereby showing excellent detection capability for weak welding defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a measuring unit constituting the welding state inspection device of the present invention.

[0030] Figure 2 It is composed Figure 1 Plan view of the bracket of the measuring unit shown.

[0031] Figure 3 It is composed Figure 1 Plan view of the upper plate of the measurement unit shown.

[0032] Figure 4 2 is a connection diagram of an upper plate and an upper guide member according to an embodiment of the present invention.

[0033] Figure 5 yes Figure 1 Front view of.

[0034] Figure 6 is a schematic diagram of a resistance measuring probe according to an embodiment of the present invention.

[0035] Figure 7 is a graph showing the correlation between welding strength and resistance.

[0036] Figure 8 is a schematic diagram illustrating a method for measuring resistance according to an embodiment of the present invention.

[0037] Fig. 9 is a schematic diagram illustrating a method for measuring resistance according to another embodiment of the present invention. DETAILED DESCRIPTION

[0038] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms and words used in this specification and claims should not be interpreted as limited to common or dictionary terms, and the inventor may appropriately define the concepts of the terms to best describe his invention. The terms and words should be interpreted as meanings and concepts consistent with the technical ideas of the present invention.

[0039] Therefore, the embodiments described in the specification and the configurations described in the drawings are only the most preferred embodiments of the present invention, and do not represent all technical ideas of the present invention. It should be understood that various equivalents and modifications may exist to replace them when the present application is filed.

[0040] Furthermore, throughout the specification, when an element is referred to as “comprising” an element, it should be understood that the element may also include other elements unless explicitly stated otherwise.

[0041] The present invention provides a device for checking the welding state in an electronically or mechanically connected welding part in a lithium secondary battery, the device comprising: a measuring unit, the measuring unit being configured to obtain data by allowing a resistance measuring probe to contact the welding part, the data being used to derive the resistance value of the welding part; and a controller, the controller being configured to communicate with the measuring unit, determine the resistance value of the welding part by receiving the data obtained from the measuring unit, and determine whether weak welding is performed by comparing the determined resistance value with a threshold resistance value, wherein the measuring unit is configured to allow the resistance measuring probe to contact one end and the other end of the welding part.

[0042] Figure 6 is a schematic diagram of a resistance measuring probe according to an embodiment of the present invention. Figure 6 , a pair of resistance measuring probes 150 and 150' of the present invention are provided, which include a pair of current probes and a pair of voltage probes. That is, one resistance measuring probe 150 includes a current probe 151 and a voltage probe 152, and the other resistance measuring probe 150' also includes a current probe 151' and a voltage probe 152'. Therefore, the resistance of the welding part can be measured by a 4-wire measurement scheme. The current probe applies a current to the welding part to be measured, and the voltage probe measures a voltage. Thus, the resistance of the welding part can be determined.

[0043] In the present invention, data for determining the resistance value is obtained by allowing a pair of resistance measuring probes to contact the welding portion. Thus, the resistance of the welding portion can be measured by a 4-wire measurement scheme. Compared with the 2-wire resistance measurement scheme, since the 4-wire resistance measurement scheme is less affected by the contact resistance, the micro resistance can be measured more accurately in the 4-wire resistance measurement scheme, and the resistance can even be measured in nanoohms in the 4-wire resistance measurement scheme.

[0044] Figure 1 is a schematic diagram of a measuring unit 100 constituting a welding state inspection device according to an embodiment of the present invention. Figure 1 The measuring unit 100 of the present invention includes: a flat bracket 110 on which an object is mounted; an upper plate 120, which is configured to be located on an upper portion having a predetermined separation distance from the bracket and includes a plurality of through holes, into which resistance measuring probes can be inserted; a lower plate 130, which is configured to be located on a lower portion having a predetermined separation distance from the bracket and includes a plurality of through holes, into which resistance measuring probes can be inserted; a coupling unit 140, which is configured to allow the flat bracket, the upper plate, and the lower plate to be coupled to each other; and a pair of resistance measuring probes 150 and 150', which are configured to obtain data for determining a resistance value by contacting a welding portion.

[0045] The support 110 is a flat rectangular member on which an object including a welding portion to be inspected is placed, and the object is mounted on a center portion. Figure 2 is a plan view of a bracket 110 according to an embodiment of the present invention. Figure 2 The bracket 110 of the present invention includes a plurality of coupling holes 111 into which coupling rods described later can be inserted, and the coupling holes are formed at four edge portions of the bracket. Further, a rectangular through hole 112 is formed on a portion corresponding to a welding portion of the object in the thickness direction of the bracket to allow the resistance measuring probe to contact the top side and the back side of the welding portion, and the welding portion is located in the region of the through hole 112.

[0046] The upper plate 120 is located at a predetermined separation distance in a vertical upward direction from the bracket 110. The upper plate is flat like the bracket, and includes a plurality of through holes into which the resistance measuring probes including a current probe and a voltage probe can be inserted. Figure 3 is a plan view of the upper plate 120 according to one embodiment. Figure 3 , the upper plate of the present invention is a flat rectangular member and has coupling holes 121 at four edge portions, respectively. In addition, a coupling rod (not shown) described later is inserted into the coupling hole. The upper plate 120 includes a through hole 122 into which the resistance measuring probe can be inserted. A plurality of through holes are formed at portions corresponding to one end and the other end of the welding portion. In this way, the resistance measuring probe can approach one end and the other end of the welding portion. In addition, the resistance measuring probe inserted into the upper plate can approach the top of the welding portion.

[0047] The lower plate 130 is located at a position with a predetermined separation distance from the bracket 110 in the vertical downward direction. Similar to the upper plate, the lower plate is a flat rectangular member and includes a plurality of through holes into which the resistance measuring probe can be inserted. The four edge portions of the lower plate respectively have coupling holes, into which the coupling rods described later are inserted. Similar to the upper plate, the lower plate has a plurality of through holes into which the resistance measuring probe can be inserted, and the through holes can be formed at portions corresponding to one end and the other end of the welding portion. Therefore, the resistance measuring probe can approach one end and the other end of the welding portion. In addition, the resistance measuring probe inserted into the lower plate can approach the back side of the welding portion.

[0048] Similarly, since the upper plate and the lower plate include a plurality of through holes into which the resistance measuring probes can be inserted, the insertion positions of the resistance measuring probes can be appropriately adjusted according to the inspection positions of the welded portions.

[0049] refer to Figure 1 An upper guide member 160 and a lower guide member (not shown) are respectively coupled to the upper plate 120 and the lower plate 130. The upper guide member 160 and the lower guide member (not shown) allow the resistance measuring probe to be inserted at a correct position.

[0050] Hereinafter, the upper guide member will be described. Figure 4 is a diagram of the connection between the upper plate and the upper guide member according to an embodiment of the present invention. Figure 4 , the upper guide member 160 includes a plurality of through holes 161 into which the resistance measuring probes can be inserted. Figure 4 In the embodiment shown in , there are two through holes, and the resistance measuring probe can be inserted into each through hole. The through holes are formed on the parts corresponding to one end and the other end of the welding part. The resistance measuring probe can be inserted into one end and the other end of the welding part, or the resistance measuring probe can also be inserted into only one end of the one end and the other end of the welding part.

[0051] In addition, the upper plate 120 has a plurality of through holes 122. The resistance measuring probe 150 sequentially passes through the through holes 161 of the upper guide member 160 and the through holes 122 of the upper plate 120, thereby approaching the upper surface of the welding portion of the object. At this time, in order to allow the resistance measuring probe to pass through all the through holes in the through holes 161 of the upper guide member and the through holes 122 of the upper plate, the through holes are placed on a straight line in the direction of inserting the resistance measuring probe, such as Figure 4Therefore, the upper guide member 160 allows the resistance measuring probe to be inserted in the thickness direction of the upper plate in a non-inclined state, and fixes the resistance measuring probe.

[0052] Although in Figure 4 , but as in the upper guide member, the lower guide member is coupled to the lower plate, and the lower guide member includes a plurality of through holes into which the resistance measuring probe can be inserted. In addition, there may be two through holes, and the resistance measuring probe may be inserted into each through hole. As in the upper plate, the lower plate includes a through hole, and the resistance measuring probe sequentially passes through the through hole of the lower guide member and the through hole of the lower plate, thereby approaching the lower surface of the welded portion of the object on the bracket. At this time, in order to allow the resistance measuring probe to pass through the through hole of the lower guide member and the through hole of the lower plate, the through hole of the lower guide member and the corresponding through hole of the lower plate are placed on a straight line in the direction of inserting the resistance measuring probe. As in the upper guide member, such a lower guide member fixes the resistance measuring probe while allowing the resistance measuring probe to be inserted in a non-inclined manner.

[0053] The bracket, upper plate and lower plate constituting the measuring unit of the present invention are connected by a connecting unit. As described above, the bracket, upper plate and lower plate include connecting holes at four edge portions, and the connecting unit includes a connecting rod and a connecting screw.

[0054] refer to Figures 1 to 5 The coupling unit 140 of the present invention is configured to allow the coupling rod 141 to be inserted through the coupling holes of the upper plate 120, the bracket 110, and the lower plate 130, thereby allowing the upper plate, the bracket, and the lower plate to be coupled to each other.

[0055] In addition, the measuring unit 100 of the present invention further includes a compression spring 170 for adjusting the separation distance between the bracket 110 and the upper plate 120 and the separation distance between the bracket 110 and the lower plate 130, and the coupling rod 141 can be inserted into the hollow portion of the compression spring 170. The upper plate 120 and the lower plate 130 can be moved along the coupling rod 141 in the vertical direction respectively by the elasticity of the compression spring 170. By applying a load to the upper plate 120 and / or the lower plate 130 in the direction of the bracket 110, the upper plate 120 and / or the lower plate 130 can be positioned at a desired position, and then the upper plate 120 and / or the lower plate 130 can be fixed at the desired position by using the coupling screw 142. In addition, the compression spring 170 can have a length corresponding to the distance from the upper plate to the lower plate of one coupling rod 141, but one coupling rod 141 can pass through two compression springs. In this case, one compression spring has a length corresponding to the length between the upper plate 120 and the bracket 110 , and the other compression spring has a length corresponding to the length between the lower plate 130 and the bracket 110 .

[0056] In a specific example, the welding state inspection device of the present invention further includes an output unit configured to display the data obtained from the measuring unit and the resistance value of the weld determined by the controller. The inspection performer can check the resistance value of the weld to be inspected through the output unit.

[0057] In a specific example, the welding state inspection device of the present invention further includes a power supply for applying power to the measuring unit. The power is preferably DC power. This is because the DC scheme has the advantage of being able to perform high-precision resistance measurement compared to the AC scheme. The controller controls the magnitude of the current applied to the measuring unit, the current application time, the time point of applying the current, and the like.

[0058] The controller described in the present disclosure will be described in detail.

[0059] The controller of the present invention communicates with the measuring unit, determines the resistance value of the welding portion by receiving data obtained from the measuring unit, and determines whether weak welding is performed by comparing the determined resistance value with a threshold resistance value.

[0060] In the inspection apparatus of the present invention, the controller includes a threshold resistance value setting program for setting the threshold resistance value by processing data obtained for the sample group by a statistical scheme.

[0061] The inventors of the present invention have found that the resistance value of a weld having a low weld strength is greater than the resistance value of a weld having a normal weld strength, which led them to the present invention. Figure 7 , the resistance value of the welded portion that has been welded with a normal welding strength of 22kgf or more is smaller than the resistance value of the welded portion that has been welded with a weak welding strength of less than 22kgf. Conventionally, there is a technology for detecting welding defects by measuring the resistance of the welded portion and comparing the measured resistance value with a threshold resistance value. However, in the conventional technology, since the correlation between the tensile strength and the resistance of the welded portion is used when deriving the threshold resistance value, a separate process for measuring the tensile strength of the welded portion is required.

[0062] However, the detection device of the present invention does not rely on the correlation between the resistance of the weld and the tensile strength, but uses a statistical scheme to derive a threshold resistance value, and accurately measures the resistance by increasing the resolution when obtaining data, thereby measuring resistance in nanoohm to microohm units to determine the resistance value of the weld.

[0063] Typically, the resistance value forms a normal distribution curve based on the data obtained for a large number of sample groups. In the normal distribution curve, from the perspective of statistical probability, an object with a large deviation may be easily assumed to be defective, and thus the predetermined deviation is determined as the threshold resistance value. In addition, this method is based on the premise that the data of the sample group is reliable. Therefore, in the process of setting the threshold resistance value, the present invention uses a measuring unit that can accurately measure the resistance of the nanoohm to microohm level for the sample group, and when measuring the resistance of the object to be inspected, the present invention uses a measuring unit that can accurately measure the resistance of the nanoohm to microohm level. Similarly, the controller constituting the inspection device of the present invention includes a program for setting the threshold resistance value by processing the data obtained by the measuring unit for the sample group with a statistical scheme. Therefore, unlike the prior art, there is no need to separately measure the tensile strength of the weld in order to set the threshold resistance threshold.

[0064] A welding defect inspection method using the inspection device of the present invention will be described in detail. The method for inspecting welding defects according to an embodiment of the present invention includes: a threshold resistance setting step (S100): measuring the resistance of the welding portion of the sample group and deriving a threshold resistance value, which becomes an evaluation standard for weak welding; a resistance measuring step (S200): measuring the resistance value of the welding portion to be inspected; and a determination step (S300): if the resistance value measured in the resistance measuring step exceeds the threshold resistance value, it is determined to be a weak welding, wherein the threshold resistance setting step (S100) and the resistance measuring step (S200) use the above-mentioned measurement unit.

[0065] First, the threshold resistance setting step (S100) will be described.

[0066] The threshold resistance setting step (S100) includes: a data construction step (S110) of determining the resistance value of the welding portion of the sample group and storing the determined resistance value; and a threshold resistance value derivation step (S120) of deriving the threshold resistance value by processing the data accumulated by the data construction step (S110) with a statistical scheme.

[0067] The data construction step (S110) includes the following process: data for determining the resistance of the welding parts of a large number of objects constituting the sample group is obtained by using the measuring unit constituting the inspection device of the present invention, and the resistance value is determined based on the obtained data. A pair of resistance measuring probes constituting the measuring unit of the present invention is allowed to contact the welding part. At this time, since one resistance measuring probe includes a current probe and a voltage probe, a pair of resistance measuring probes includes a pair of current probes and a pair of voltage probes. Therefore, a 4-wire resistance measurement can be performed. Compared with the 2-wire resistance measurement scheme, the 4-wire resistance measurement scheme has the advantage that the contact resistance is small, so that data can be obtained more accurately.

[0068] In the data construction step (S110), the number of objects in the sample group is at least 100,000, preferably 200,000, and in terms of reliability, it is preferred to have as many objects in the sample group as possible.

[0069] The threshold resistance value derivation step (S120) includes derivation of the threshold resistance value by processing the data accumulated by the data construction step (S110) in a statistical scheme. The controller constituting the inspection device of the present invention includes a program for setting the threshold resistance value by processing the data in a statistical scheme. In a specific example, the program can obtain a normal distribution curve of the corresponding resistance values ​​of the objects of the sample group, and in the normal distribution curve, the sum of the average value of the resistance value and 6δ can be set as the threshold resistance value.

[0070] When the sample group presents a normal distribution curve, the values ​​of most objects are close to the average value (u), and only a few objects deviate significantly from the average value (u). Therefore, objects with values ​​that deviate significantly from the average value can be randomly assumed to be defective. Specifically, the probability of an object with a deviation of 1δ (standard deviation) occurring is about 32%, the probability of an object with a deviation of 2δ occurring is about 5%, the probability of an object with a deviation of 3δ occurring is about 0.3%, the probability of an object with a deviation of 4δ occurring is about 0.01%, the probability of an object with a deviation of 5δ occurring is about 0.001%, and the probability of an object with a deviation of 6δ occurring is about 0.0000001%. Therefore, even if the sum of the average value and 6δ is set as the threshold resistance value, and it is assumed that a resistance value greater than the sum indicates that weak welding has been performed, the reliability is very high.

[0071] Hereinafter, the resistance measuring step (S200) will be described in detail. The resistance measuring step (S200) includes obtaining data for determining the resistance value of the welded portion to be inspected by the measuring unit constituting the inspection apparatus of the present invention.

[0072] The measuring unit according to the present invention includes two resistance measuring probes, and obtains data for deriving a resistance value by allowing the two resistance measuring probes to contact a welding portion. Figure 8 is a schematic diagram showing a process of acquiring data using a resistance measurement probe according to an embodiment of the present invention. Figure 8 , one resistance measuring probe 150 is allowed to contact one end 31 of the soldering portion 30, and the remaining one resistance measuring probe 150' is allowed to contact the other end 32 of the soldering portion 30, thereby measuring the entire resistance of the soldering portion 30. Figure 8 In the embodiment of the present invention, two resistance measuring probes 150 and 150' are located on the upper surface of the welding part. Figure 8 As shown in , the welding portion 30 may be divided into a welding portion 33 of the electrode tab 20 and a welding portion 34 of the electrode lead 10, and both resistance measuring probes may be allowed to contact the welding portion 33 of the electrode tab. Alternatively, both resistance measuring probes may be allowed to contact the welding portion 34 of the electrode lead.

[0073] Fig. 9 FIG. 1 is a schematic diagram showing a process of acquiring data using a resistance measuring probe according to another embodiment of the present invention. Fig. 9, one resistance measuring probe 150 may be allowed to contact the welding portion 33 of the electrode tab portion, and the remaining one resistance measuring probe 150' may be allowed to contact the welding portion of the electrode lead portion, thereby performing resistance measurement. In the above embodiment, from the viewpoint of the detection capability of detecting weak welding, it is most preferred to measure the resistance in the form of contacting two resistance measuring probes on the welding portion 33 of the electrode tab portion.

[0074] The welding state inspection device and welding defect inspection method of the present invention can be widely applied to the welding parts of secondary batteries, and can be applied to welding parts according to various welding schemes. That is, the welding defect inspection method of the present invention can be applied to the welding parts between electrode tabs and electrode tabs in the battery pack, the welding parts between electrode tabs and electrode leads, and the welding parts between electrode leads and bus bars, and can also be applied to welding parts of ultrasonic welding and laser welding, etc.

[0075] According to the welding state inspection device of the present invention, the resistance of the sample group is measured, and the threshold resistance value is set by the normal distribution curve of the measured resistance value. When measuring the resistance of the sample group and the welding part to be inspected, the resistance is accurately measured by using a micro-resistance measuring instrument with a resolution of nano-ohm to micro-ohm level, thereby showing excellent detection capability for weak welding defects.

Claims

1. An apparatus for inspecting a welding state in a welding portion for electronic or mechanical connection in a lithium secondary battery, comprising: a measuring unit configured to obtain data for deriving a resistance value of the welding portion by allowing a resistance measuring probe to contact the welding portion; and a controller configured to communicate with the measuring unit, determine a resistance value of the welded portion by receiving the data obtained from the measuring unit, and determine whether weak welding is performed by comparing the determined resistance value with a threshold resistance value, wherein the measuring unit is configured to allow the resistance measuring probe to contact one end and the other end of the welding portion, Wherein, the measuring unit comprises: a flat stand on which the object is mounted; an upper plate configured to be located on an upper portion having a predetermined separation distance from the bracket and including a plurality of through holes into which the resistance measuring probes can be inserted; a lower plate configured to be located on a lower portion having a predetermined separation distance from the bracket and including a plurality of through holes into which the resistance measuring probe can be inserted; a coupling unit configured to allow the bracket, the upper plate, and the lower plate to be coupled to each other; and a pair of resistance measuring probes configured to obtain data for determining a resistance value by contacting the welding portion, Wherein, the connecting unit includes a connecting rod and a connecting screw, the bracket, the upper plate and the lower plate each have connecting holes at four edge portions, and when the connecting rod passes through the connecting holes formed on the upper plate, the bracket and the lower plate in sequence, the upper plate, the bracket and the lower plate are connected.

2. The device according to claim 1, wherein: If the determined resistance value exceeds the threshold resistance value, the controller determines that weak welding is performed.

3. The device according to claim 1, wherein: A resistance measurement probe consists of a current probe and a voltage probe.

4. The device according to claim 1, wherein: Upper and lower guide members for allowing the resistance measuring probe to be inserted into a correct position are coupled to the upper and lower plates, respectively.

5. The device according to claim 4, wherein: The upper guide member and the lower guide member respectively have through holes into which the resistance measuring probe can be inserted, wherein the through hole of the upper guide member and the through hole of the upper plate are located in a straight line, thereby allowing the resistance measuring probe to pass through the through hole to approach the upper surface of the welding portion, and The through hole of the lower guide member and the through hole of the lower plate are located on a straight line, thereby allowing the resistance measuring probe to pass through the through hole to approach the lower surface of the welding portion.

6. The apparatus according to claim 1, further comprising a compression spring for adjusting a separation distance between the bracket and the upper plate and a separation distance between the bracket and the lower plate, in, The coupling rod is configured to be insertable into the hollow portion of the compression spring.

7. The device according to claim 1, wherein: The controller includes a threshold resistance value setting program for setting the threshold resistance value by processing data obtained for a sample group in a statistical scheme.

8. The device according to claim 7, wherein: The resistance values ​​determined from the data obtained for the sample set form a normal distribution curve.

9. The apparatus according to claim 1, further comprising a power supply configured to apply power to the measuring unit, in, The power is direct current (DC) power, and is controlled by the controller.

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